The invention relates to fishing, and more particularly to a method and apparatus for capturing tuna by purse seining while separating and releasing substantially all porpoise captured along with the tuna.
In the recent past the tuna fishing industry has been nearly completely transformed from the use of the bait and line method to the use of large nets or seines which draw together or purse at their deep ends to trap whole schools of tuna. These purse seines are usually about one half mile long and about 350 feet in depth. They are set by a seiner, or fishing boat adapted for use of the seine, along with a skiff which tows the leading or bunt end of the seine out from the seiner to encircle the school of tuna. When the set is complete both ends of the seine are retained to a side of the seiner, the seine being supported by a corkline or float line attached to its upper side. At intervals along the deep edge of the seine are purse rings which support a purse line, both ends of which are held at the seiner. The purse line is drawn to purse the bottom of the net and trap the school of fish.
To harvest the catch the rear or hauling end of the seine is progressively hauled aboard the seiner while corresponding purse rings are released in sequence to enable the net to be stacked in an ordered fashion on the deck. The net remaining in the water is thus shortened to a greater and greater extent, concentrating the fish into a diminishing space. When only a small fraction of the seine remains, it is gathered alongside the seining vessel and the adjacent skiff to "sack up" the catch, concentrating perhaps 40 to 50 tons of fish into a very small pocket of the net between the seiner and the skiff.
The sacked fish are then hauled or brailled out of the net and into tanks aboard the seiner by a dipping net known as a brail. When the operation is completed the remainder of the seine is hauled aboard, with corresponding purse rings released in sequence as described above, and stacked on the deck. Since the bunt end of the seine is brought aboard last, the seine is prepared for the next set.
The above seine fishing method and apparatus are fully described, explained and illustrated in the article, "Purse Seine Revolution in Tuna Fishing," Richard L. McNeely, Pacific Fisherman, Vol. 59 No. 7 (June 1961).
A principal method of finding schools of tuna, particularly Yellowfin tuna in tropical waters, is to locate groups of porpoise, which commonly associate with schools of Yellowfin tuna. Being marine mammals, the porpoise breathe air and thus tend to remain close to the surface. The tuna intermix with the porpoise for reasons which are not fully understood. Although this sometimes helps fishermen in locating tuna, it also gives the fishermen serious problems in that porpoise are inevitably captured along with the school of tuna as the seine is pursed, hauled and sacked. Large numbers of porpoise are often injured and killed with the tuna catch. The fins of the porpoise become entangled in the net, which usually has about a 4-inch mesh, and many are held below the water surface for prolonged periods, causing drowning. Many are thought to die merely from shock as they frantically attempt to escape the ever-diminishing net enclosure. It has been estimated that as many as 300,000 porpoise per year have been killed incidental to the tuna seining activities of U.S. fishermen.
Primarily in response to the legal requirements of the federal Marine Mammal Protection Act of 1972 (16 U.S.C. paragraph 1361), seining tuna fishermen have attempted to reduce this incidental porpoise mortality. The Act mandates that incidental porpoise kill be lowered to near zero with quota-type limits imposed. Of course it is also in the interests of the fishermen to reduce the kill rate, since serious depletion of porpoise stocks may adversely affect their ability to locate tuna.
One method which has been used by seiners in an effort to release porpoise from the net, once encircling maneuvers have been completed, is "backing down" or reversing the seining vessel to pull the most remote portions of the net under the water surface, thereby attempting to allow porpoise to pass over the corkline of the net in this area. Since tuna also try to escape the net along with the porpoise, the vessel must perform a series of backing down and stopping maneuvers, so that the net can be allowed to return to the surface via its corkline after each backing down. Net tenders in auxiliary boats must be used to assist the porpoise out and help raise the net to stop the escape of tuna.
By another method several seine skiffs, or auxiliary boats, have been used to pull outwardly at several points on the perimeter of the net to keep it in an open configuration so that it does not collapse or fold over upon itself to entrap and drown porpoise. Also, removal of the porpoise by hand during sacking up has often been resorted restored to. This involves members of the crew in skiffs alongside the net.
Gear modifications seeking to reduce incidental porpoise kill have included the extensive use of small-mesh netting in the seine to avoid the snagging of porpoise fins, flippers and snouts as the porpoise attempt to escape. A more limited modification has been the installation of a "Medina Panel" of small-mesh netting only in the center of the net for a depth of about 100 feet. The purpose of the panel, which has usually included about 1 1/4-inch mesh instead of the usual 4 1/8-inch mesh, was to prevent the entanglement of porpoise in the net during backing down maneuvers.
Seining crews have also experimented with socalled "large volume" or more extensive nets to provide more water surface area, in conjunction with pulling outwardly at several points on the net to prevent folding over of portions of the net as discussed above. This type net and the accompanying method were also supposed to help prevent porpoise from being snagged, trapped and drowned.
Although these methods and gear modifications have reduced porpoise kill to some extent, their success has been very limited. Moreover, the described methods have involved inordinate amounts of labor and time and have been very costly to the tuna fishing industry. In spite of the difficulty and expense of these attempts to solve the porpoise problem, the goals of the Marine Mammal Protection Act have not been met.